1. Field of the Invention
The present invention relates to a method for preadjusting and controlling the strip planarity in flexible single-pass and reversing rolling of a strip-shaped material web by means of at least one pair of work rolls which form a roll gap and associated back-up rolls as well as devices for roll adjustment, roll bending, roll displacement and roll balancing.
2. Description of the Related Art
The continuous improvement of environmental conditions, the scarcity of raw materials, and the requirement that the industry inexpensively manufacture structural components of different types with optimum properties which are specific with respect to the product, require the development of new manufacturing methods. Among these is the so called xe2x80x9cflexible rollingxe2x80x9d whose object it is to manufacture rolled products with cross-sectional shapes which are optimized with respect to load application and weight. Flexible rolling, in which the roll gap is regulated during the rolling process in accordance with the thickness profile of a rolled strip which changes over the strip length, facilitates the manufacture of strip material having a thickness profile which is precomputed and component-specific and adapted to the respective load application, wherein the thickness profile changes in the rolling direction, and wherein this manufacture reduces the length of the processes. A rolled strip manufactured of steel and non-iron metals is suitable for light-weight construction in the fields of automobile construction, aircraft and spacecraft technology and rail car construction (DE-Z Fertigung, 1995, Volume 23, Issue 10, pages 40-42).
In conventional rolling, it is desirable to produce a strip which is as flat as possible without any changes of the profile over the entire strip length. In flexible rolling, on the other hand, controlled strip thickness changes over the strip length are to be manufactured while maintaining the strip planarity over the strip width. Methods for producing flat strips with constant strip thicknesses are known in the prior art. However, for maintaining the strip planarity over the strip width, additional special preadjustment measures are required in the entire area of the strip thickness changing ramp. The possible strip thickness reduction can take place in a range between a small reduction which still maintains a stable rolling process and a maximum reduction of more than 50%.
DE 100 36 564 C2 describes a multi-roll stand for the flexible rolling of strip material with a control of the work roll bending devices in dependence on the rolling force and the strip width. With increasing pass reduction and the resulting increase of the rolling force over the thickness profile ramp produced by flexible rolling in the rolling direction, the positive bending force at the work rolls is increased in order to compensate for the portion of the increasing roll bending. This is part of the control of the strip planarity over the strip width. Conversely, when the pass reduction is decreased, the positive work roll bending is again reduced. For increasing the effectiveness of the work roll bending, the back-up rolls are displaceable independently of each other in the axial direction by equal or different distances relative to the vertical middle plane of the roll stand for compensating the occurring roll bending and for adjustment to the strip width.
In a method for flexible rolling of a metal strip disclosed in DE 100 37 867 A1, during each adjustment of the roll cap or immediately thereafter, the elastic lines of the work rolls are controlled in dependence on the adjusted roll gap for achieving a planarity of the metal strip.
DE 197 13 004 A1 is directed to a method for preadjusting and controlling the planarity of a continuously rolled strip of uniform thickness in which the roll gap profile is determined by nominal values for the roll gap profile with the aid of a roll gap model and, without knowing the precise functional relationships between the variables strip thickness, strip width, work roll diameter and rolling force, the precomputed roll gap profile or an equivalent variable is adjusted or adapted with a correction value.
DE 43 31 261 C2 describes possibilities for an asymmetrical work roll bending control for conventional rolling of strip-shaped rolled material of uniform thickness for achieving a flat material web by using pairs of bending forces having the same total magnitude, wherein the bending forces of each pair have the same or different magnitudes and act in the same or opposite directions.
It is the primary object of the present invention to develop a method for the preadjustment and control of the strip planarity in flexible rolling of a strip-shaped material web with thickness-profiled ramps in each strip length section in the rolling direction over the strip width.
Starting from the method for preadjustment and control of strip planarity in flexible single-pass and reversing rolling of a strip-shaped material web, the object is met in accordance with the present invention when rolling a thickness ramp for adjusting a desired strip profile shape over the strip width, by determining the corresponding adjustment parameters by accessing on line a multidimensional data matrix produced off line by means of a FEM model for all adjustment ranges of the rolling force, the roll displacement and the bending control at all occurring strip widths.